This invention concerns a two-way information transmission system between a mobile station and a ground control station; the term information being understood to means analog and/or digital signals corresponding in a general way to sounds, pictures, instructions, measurements, etc.
The mobile station, which moves along a known path, may be for example a train, a funicular, an elevator, an automobile, a containment shell inspection truck, etc. The control station is on the ground and stationary.
Transmissions are effected for example through a waveguide disposed along the path followed by the mobile station, equipped with a transmitting and receiving antenna, moving alongside the waveguide. A waveguide transmission system is described in the article "Waveguide Communication System for Centralized Railway Traffic Control" by T. Kawakami et al, IEEE Trans. on Vehicular Communications, Sept. 1964, pp. 1-18. The article entitled "High Frequency Guided Electromagnetic Waves in Application to Railway Signalling and Control", by H. M. Barlow, in The Radio and Electronic Engineer, May 1967, pp. 275-281, also discusses the use of microwaves for locating trains and for telephone communications. These articles essentially concern the problem of transmission of a microwave by a waveguide alongside a railroad and an antenna on the railway vehicle and do not discuss the transmission system, in order words the transmitter-receiver equipment on the ground and aboard the moving vehicle. They merely indicate that the frequencies allocated for the vehicle-to-ground transmission direction are lower than those allocated for the ground-to-vehicle transmission direction, and that a separate channel is assigned to television transmission in the ground-to-vehicle direction.
The presence of several frequencies corresponding to the transmission channels allocated to the different transmissions causes interferences which disturb the transmissions, such that the latter can become unusable.